41C - Email address - CodeForces Solution

#include <bits/stdc++.h>
using namespace std;
int main()
{
    string s;
    cin >> s;

    for (int i=1; i<s.size()-3;i++)
    {
        if (s[i]=='d'&& s[i+1]=='o' && s[i+2]=='t') {s[i]='.'; s.erase(i+1, 2);}
    }

    for (int i=1; i<s.size()-2;i++)
    {
        if (s[i]=='a' && s[i+1]=='t') {s[i]='@'; s.erase(i+1, 1); break;}
    }

    cout <<s;



    return 0;
}